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52 Y.A. SOYADI, Y.A. SOYADI, Y.A. SOYADI ve Y.A. SOYADI

The craft’s weight and center of gravity limits are based on a hoisting weight, speed, stability
and seakeeping requirements. The maximum allowable center of gravity is mostly limited by the
wind heel criteria. [7].

The structural design of a high speed, self-righting, rescue boat presents some unique problems.
As with any high speed craft, the designer is faced with seeking an appropriate balance between
craft weight limits and structural integrity under the expected operating conditions and service
life. The extreme operating environment, severe mission demands and extended annual
operating hours for crafts make achieving an appropriate balance a challenging task. As a
general design of high speed craft is based on the idea that the structural design limit exceeds
the crew’s ability to sustain the maximum expected craft motions. Even though determining the
crew’s operational limits is subjective some reasonable assumptions can be made. However, in
the case of heavy weather motor lifeboat operational limits are at best uncertain. In the surf
rescue motion and the magnitude of the loads on the craft are now well known or predictable.
An overly conservative design approach might be indicated owing to the uncertainty but, the
weight constraints required for high speed performance necessitates a weight conscience
structural design approach.

Key design considerations in the coupling and shafting arrangement included minimizing the
coupling joint angles to maximize reliability and locating the engines and gears low in the hull
to reduce the KG and increase stability. The parallel arrangement of shaft configuration usually
favored because it offers substantial benefits with respect to producibility and alignment.

The heating, ventilation and air conditioning (HVAC) system is required to maintain
temperatures between 13°C and 27°C in enclosed bridge and 26°C to 27°C in the survivor’s
compartment with external air temperatures ranging from -12°C to 37°C. The systems use direct
expansion Freon with reverse cycle heating. While the design is relatively conventional,
requirements for self-righting and the need to avoid progressive flooding in a damaged
condition present special design considerations. Much like the engine air intake, the design of
HVAC intakes and exhausts require special attention at various roll angles.

With watertight integrity essential for vessel safety, all doors. Hatches and windows fitted to
self-righting craft must be capable of resisting the hydrostatic forces associated with capsize. In
addition, most will be fitted in compartments or spaces used as part of the vessel’s watertight
subdivision, so could be required to keep water in as well as out. All doors, hatches and
windows fitted to self-righting craft must therefore be as strong as the adjacent structure and
capable of accepting hydrostatic pressure from either side. No door, hatch or window can be
expected to do its job of keeping water out if not securely closed, so to minimize the risk to
vessel safety, all should be kept shut at sea unless actually being used. Those that do need to be
opened regularly for crew access to other parts of the vessel, such as wheelhouse doors onto the
deck, should remain open for the shortest possible time and must consequently be quick and
easy to operate with a positive and secure locking mechanism. Wheelhouse doors on rescue
vessel are often located facing aft to protect them from direct wave impact. Even modern
lightweight composite doors can inflict serious injury when driven by a heavy roll, so it is
important to provide grab rails adjacent all doors to discourage crew members from using the
door frame as a handhold when moving around the vessel.

GiDB|DERGi Sayı 6, 2016